1. Field of the Invention
The present invention relates a flat membrane element and a regeneration method thereof, and specifically to, a flat membrane element used to filtrate water to be processed and a regeneration method thereof.
2. Description of the Related Art
A flat membrane element of this kind is set in water to be processed in a dipped manner and used to filtrate the water to be processed. FIG. 7 is a partial sectional view showing a general structure of a flat membrane element. A support plate 1 is formed such that a circumferential edge 2 thereof has a flame shape and a water passing portion 3 is formed in the inner portion thereof. A membrane sheet 4 is attached onto both the faces of the support plate 1, respectively. A suction port 5 is connected with the circumferential edge 2. In addition, the outer surface of the circumferential edge 2 and the membrane sheet 4 have a joint portion 6 formed by lapping each other. By effecting negative pressure in the suction port 5 or by effecting positive pressure from the outer surface of the membrane sheet 4, the water to be processed is filtrated and the filtrated water penetrated through the membrane sheet 4 is discharged from the suction port 5 via the water passing portion 3. Note that the water passing portion 3 of the support plate 1 is specially treated to have a figure through which the filtrated water can pass freely while supporting the surface of the membrane sheet 4 to prevent the attached membrane sheet 4 from sagging.
The membrane sheet 4 is called, for example, an ultrafiltration membrane or an ultrafilter membrane, and that made of synthetic resin is used in general. Also, as for the support plate 1, that made of synthetic resin, which shows a favorable joint characteristic with the membrane sheet 4, is used. It is important for the flat membrane element to ensure watertightness of the joint portion 6, so that a method of jointing the support plate 1 and the membrane sheet 4 with an adhesive is widely employed. However, the method of using the adhesive easily causes deviation in adhesive force in addition to the problems that the adhesive deteriorates easily to lower the watertightness and that leak from the lateral direction of the membrane sheet 4 is easily caused.
As a method of improving the problem in the jointing method using the adhesive, a flat-membrane-element manufacturing method in which a membrane sheet is deposited on a support plate by lapping the membrane sheet and the support plate each other and emitting a laser to the mutually jointed portion is disclosed in Japanese Patent Application Laid-Open No. 2005-279580. In this method, the membrane sheet is made of a material having larger laser penetration and the support plate is made of a material having larger laser absorption property, in which the membrane sheet is deposited on the support plate by emitting a laser from the membrane sheet side to the joint portion while pressing the membrane sheet toward the support plate. In the method disclosed in Japanese Patent Application Laid-Open No. 2005-279580, the flat membrane element in which the joint portion has strong adhesive force and the leak from the lateral direction along the adhered surface of the membrane sheet are hard to be caused, can be manufactured at relatively low costs.
The above-described flat membrane element causes an extreme clogging in the membrane sheet or the membrane sheet is damaged to be unable to hold a normal filtrating function when it filtrates the water to be processed for a long period of times. Although the spent flat membrane element over durable years as described above is normally processed or disposed as an industrial waste, it sometimes causes an environmental contamination when discarded. Further, in the flat membrane element, the material and processing costs of the support plate is overwhelmingly high as compared with the membrane sheet, and when the expensive support plate is thrown out as an industrial waste, the regeneration cost of the flat membrane element increases, posing a problem. Therefore, as a measure, it is conceivable that the membrane sheet over the durable years is pulled out and peeled from the support plate to reuse the support plate. However, the deposited portion of the membrane sheet and the support sheet which is deposited by the laser emission is rigid requiring many labor hours and costs to be pulled and peeled, being unadvisable.
As a measure improving the problem as described above, in Japanese Patent Application Laid-Open No. 2000-107576, a regeneration method of a flat membrane element by way of recovering, in which a major part of the membrane sheet (filtration membrane) other than the deposited portion is cut from a spent flat membrane element (membrane cartridge) and, after that, a new membrane sheet is adhered in a lapping manner onto the deposited portion of the membrane sheet of the former support plate (filtration plate), is disclosed.
However, the regeneration method of the flat membrane element disclosed in Japanese Patent Application Laid-Open No. 2000-107576 has a large difference in view of a fixing method of the membrane sheet between the case where a membrane sheet is deposited onto a support sheet when manufacturing a new product and the case where membrane sheets are adhered to each other when regenerating the product, causing a cost increase due to an additional manufacturing line required. Further, there arise differences between the new product and the regenerated product in view of durability and reliability, indicating a possible degradation of the regenerated product in the commercial value.